With the development of communication network technologies and the rapid popularization of the Internet, categories, formats and service demands of network information flows become more and more abundant, and the data transport network gradually becomes unable to deal with the dispatching and switching of services of the transport layer effectively. The primary technologies adopted in the data transport network are the Synchronous Digital Hierarchy (SDH) technology, the Asynchronous Transfer Mode (ATM) technology, the Multiple Service Transport Platform (MSTP) technology and the Wave-length Division Multiplexing (WDM) technology. Therefore, the transport network urgently needs a transport ring network technology which can carry multiple types of services uniformly, provide better Quality of Service (QoS) and be extended flexibly, and is applicable to both the Metropolitan Area Network (MAN) and the Wide Area Network (WAN). In this case, a ring network based on an MPLS protocol appears.
The key of the MPLS protocol is the introduction of a Label, whose information content is short and easy to be dealt with, with local meaning and without topology information. The Label is short, thus easy to be dealt with, and may be cited directly by an index generally, and since the Label only has the local meaning, it is easy to be assigned.
In an MPLS network, a packet is encapsulated with the Label by an MPLS edge device when entering a first MPLS device. The MPLS edge device selects an appropriate Label for the packet by analyzing the content of the packet. Specifically, the MPLS edge device analyzes not only destination address information in the header of the packet but also other information in the header of the packet. And, all the nodes in the MPLS network determine whether to forward the packet according to a Label assigned. Thus, the MPLS network forwards a packet much faster than an IP network does. The Label will be separated by an edge device when the packet leaves the MPLS network.
Such a new MPLS network of ring type that applies to the transport layer is referred to as an MPLS ring network. To guarantee the reliable operation of the MPLS ring network, it requires that the MPLS ring network have a function of discovering topology structure automatically to enable each node in the network to acquire states of other nodes in the network in real time. However, there is not a perfect function of discovering topology structure automatically in the MPLS ring network yet at present.